The term "complex oxide ceramic" is applied to compositional states of matter that are composed of two or more metal oxide components that have been reacted to form a solid contiguous mass of crystalline grains comprised in whole or in part of the metal oxide components. The term "ultrafine subdivision" is interpreted to mean a level of mixing among the metal oxide components in which each component metal oxide is broken from a particulate state to its irreducible molecular basis and homogeneously mixed with other components that have been so equally subdivided. The term "intermediate phases" is interpreted to mean those crystalline phases of a ceramic oxide with a complex bulk composition that must first be formed from an amorphous phase of the ceramic and subsequently reacted to form a single crystalline phase of the complex ceramic. The term "fully equilibrated" is interpreted to mean the state achieved when all the intermediate phases of a complex ceramic oxide have been reacted and fully dissolved into the single crystalline phase of the complex ceramic. The term "phase equilibration" is interpreted to mean the process by which a complex ceramic becomes fully equilibrated. The term "spray pyrolysis" is interpreted to mean the process by which a solid oxide is formed directly from an aerosol salt solution on the surface of heated substrate by thermally decomposing the salts on the substrate surface and simultaneously evaporating the solution solvent. The term "integral operating element" is interpreted to mean a component of a system, without which the system would fail to perform as designed. The term preform is interpreted to mean a structure of larger cross-sectional size containing a pattern or arrangement of distinct material compositions that is extruded or drawn into a structure of smaller cross-sectional size that contains the same relative pattern or arrangement of distinct material compositions as the larger structure but reduced in scale. The term "insulating ferroelectric ceramic" is applied to a class of ceramics that have strong dielectric properties. The term "electrically conductive ceramic" is applied to a class of ceramic that is capable of transporting electrical current, of which superconductors are a subset. The term "piezoelectric ceramic" is applied to ceramics that expand or contract in volume when under the influence of an electric field, or induce an electrical voltage when under the influence of mechanical stress. The term "magneto-sensitive ceramic" is applied to ceramics that exhibit altered physical properties, such as changes in their electrical resistance, or changes in their structural characteristics under the influence of an applied magnetic field. The term "thermally insulating ceramic" is applied to ceramics that impede the flow of heat through their bodies or over their surfaces. The term "superconductivity" is applied to the phenomenon of immeasurably low electrical resistance, simultaneously occurring with the onset of diamagnetism, exhibited by materials that have been cooled to temperatures below a critical transition-temperature (T.sub.c) at which the material abruptly loses its electrical resistance and acquires diamagnetic properties not exhibited at temperatures above its T.sub.c. T.sub.c is distinct to a superconducting material's chemical composition, and is often used to rank the superconductor on a scale of cryogenic suitability. Low-T.sub.c superconductors are usually metals with critical transition-temperatures of 23 K or less. High-T.sub.c superconductors are complex copper oxide ceramics with critical transition-temperatures that can be significantly above 23 K.
Complex ceramics are often classified in terms of crystallographic structure. Ceramics possessing the physical properties described above have either spinel-type, perovskite, ilmenite, crystallographic structures, or a crystallographic structure that is recognized as a derivative of said crystallographic structure. Spinel-type crystals have a general chemical formula of AB.sub.2 O.sub.4, where O is an oxygen atom and A and B are metal atoms. In magnesium aluminate, MgAl.sub.2 O.sub.4 (spinel), the oxygen ions are configured in face-centered cubic close packing structures. In a subcell of this structure there are four atoms, four octahedral interstices, and eight tetrahedral interstices. This makes a total of twelve interstices to be filled by the three cations, one divalent and two trivalent. Two types of spinel occur. In normal spinel the A.sup.2+ ions are on tetrahedral sites and the B.sup.3+ are on octahedral sites. Examples include ZnFe.sub.2 O.sub.4, CdFe.sub.2 O.sub.4, MgAl.sub.2 O.sub.4, etc. In inverse spinels, the A.sup.2+ and half of the B.sup.3+ ions are on octahedral sites; the other half of the B.sup.3+ are on tetrahedral sites, as a B(AB)O.sub.4 crystal. This is a more common structure and used to classify the following types of ferrite crystals useful for their magnetic properties: such as, FeMgFeO.sub.4, FeTiFeO.sub.4, Fe.sub.3 O.sub.4, ZnSnZnO.sub.4, and FeNiFeO.sub.4.
Most ceramic oxide structures are based on close packing of oxygen ions. Perovskite crystals contain large cations which form a close-packed structure along with the oxygen ions. In perovskite, CaTiO.sub.3, the alkaline earth metal cations (Ca.sup.2+) and the oxygen (O.sup.2-) ions combine to form a close-packed cubic structure with a smaller, more highly charged transition-metal (Ti.sup.4+) in octahedral interstices. Each O.sup.2- ion is surrounded by four alkaline earth metal cations (Ca.sup.2+) and eight O.sup.2- ions; each alkaline earth metal cation (Ca.sup.2+) is surrounded by twelve O.sup.2- ions. In the center of the face-centered cubic unit cell the small, highly charged transition-metal ion (Ti.sup.4+) is octahedrally coordinated to six O.sup.2-. Perovskite crystals may be simple structures with two metal oxide components, CaTiO.sub.3, SrTiO.sub.3, BaTiO.sub.3, SrSnO.sub.3, LaAlO.sub.3, CaZrO.sub.3, SrZrO.sub.3, and YAlO.sub.3 ; or they may be more complex blended structures: (Ba,Sr)TiO.sub.3, Pb(Zr,Ti)O.sub.3, YBa.sub.2 Cu.sub.3 O.sub.7-.delta., Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8, or Bi.sub.1.80 Pb.sub.0.40 Sr.sub.1.91 Ca.sub.2.03 Cu.sub.3.06 O.sub.10-.delta., et cetra.
The ilmenite, FeTiO.sub.3, structure is a derivative of the corundum, Al.sub.2 O.sub.3 or Fe.sub.2 O.sub.3, structure. Derivative structures exhibit the symmetry and regularity of some simpler structure that has been perturbed to produce a more complex array of atoms. These perturbations include the ordered substitution of several different species of atoms, the ordered omission of atoms, the addition of an atom to an unoccupied site, and the distortion of the atomic array. In ilmenite, half the cation sites are occupied by Fe.sup.3+ cations, the other half by Ti.sup.4+ cations in alternate layers. This structure describes MgTiO.sub.3, NiTiO.sub.3 and MnTiO.sub.3. LiNbO.sub.3 is an example of a derivative structure in which each layer of cations contains an ordered arrangement of Li and Nb. High-T.sub.c ceramic superconductors may be considered as examples of derivative perovskite crystal structures in which cations have been arranged in organized layers.
Some of these ceramics do not naturally occur in nature. Many of these ceramics are found in nature. Technologically useful structures are made if these materials can be applied to metals and formed into mechanically workable sheets or elongated wire forms. The performance of a single such structure may be enhanced if it contains more than one type of such ceramic. High-T.sub.c superconductivity in the cuprate ceramics was first discovered in 1985. Since then, reports of high-T.sub.c superconductivity has been reported in chemical compositions that are now classified as rare-earth alkaline earth copper oxides ("RE-AE-Cu--O"):
P-1
J. G. Bednorz and K. A. Muller, "Possible High-T.sub.c Superconductivity in the Ba--La--Cu--O System", Z. Phys. B.--Condensed Matter, Vol. 64, pp. 189-193 (1986), which reveals that polycrystalline compositions of ceramics comprising oxides of elemental lanthanum, barium, and copper o exhibiting superconducting transition temperatures in the 30 K range;
P-2
R. J. Cava, R. B. van Dover, B. Batlog, and E. A. Reitman, "Bulk Superconductivity at 36 K in La.sub.1.8 Sr.sub.0.2 CuO.sub.4 ", Physical Review Letters, Vol. 58, No. 4, pp. 408-410, which reports high-T.sub.c superconductivity in cuprate ceramics comprising oxides of elemental lanthanum, strontium, copper;
P-3
M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu, "Superconductivity at 93 K in a New mixed Phase Y--Ba--Cu--O Compound System at Ambient Pressure", Physical Review Letters, Vol. 58, No. 9, pp. 908-910, March 2, 1987, which reports high-T.sub.c superconductivity in cuprate ceramics comprising oxides of elemental yttrium, barium, and copper.
High-T.sub.c superconductivity is also observed in material systems that are classified as heavy-metal mixed alkaline earth copper oxides ("HM-AE.sub.1 -AE.sub.2 -Cu--O"):
P-4
H. Maeda, Y. Tanaka, M. Fukutomi, and Y. Asano, "A New High-T.sub.c Superconductor Without a Rare Earth Element", Japanese Journal of Applied Physics, Vol. 27, No. 2, pp. L209-L210, which reports high-T.sub.c superconductivity in cuprate ceramics comprising oxides of elemental bismuth, strontium, calcium, and copper.
P-5
Z. Z. Sheng and A. M. Hermann, Nature, Vol. 332, p. 55 (1988), which reports high-T.sub.c superconductivity in cuprate ceramics comprising elemental oxides of thallium, barium, strontium, and copper.
A variety of other ceramics that exhibit insulating ferroelectric, piezoelectric, electrically conductive, magneto-sensitive, insulating, and processes used to make them from precursor powders have been well known for many years:
P-6
W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, "Introduction to Ceramics, 2nd Edition", John Wiley and Sons, New York, Copyright 1960 and 1976, discusses the existence of and methods to prepare insulating, electrically conducting, magneto-sensitive, and piezoelectric ceramic.
A common trait of ceramics with spinel, perovskite, or ilmenite crystal structures and their derivatives is that an essential property of the ceramic is anisotropic relative to its crystalline c-axis. That is, a preferred property that is essential to the proper functioning of a device may only be active or pronounced along a preferred crystallographic orientation of the ceramic. For instance, a high-T.sub.c superconducting ceramic will efficiently transport electrical current along the crystallographic a-b plane of the ceramic, and exhibit much poorer electrical conduction if the current is directed along the ceramic c-axis. Some magneto-sensitive ceramics will only change their properties if the applied magnetic field is directed along the c-axis of the ceramic.
It is thus important to exercise control over the alignment of the crystallographic c-axis throughout the bulk of the ceramic when fabricating a device of macroscopic dimension that has operational performance conditional on an orientation sensitive property of the complex ceramic. The case is clearly illustrated for high-T.sub.c superconducting ceramic in which the electrical current carrying capacity is greatly diminished when the ceramic is not properly oriented with the direction of electrical current flow throughout the bulk of the device. Critical current densities directed perpendicular to the ceramic a-axis are generally 2-3% of the electrical capacity available along orientations perpendicular to the ceramic c-axis:
P-7
S. R. Foltyn, P. Triwari, R. C. Dye, M. Q. Le, and X. D. Wu, "Pulsed laser deposition of thick YBa.sub.2 Cu.sub.3 O.sub.7-.delta. films with J.sub.c &gt;1 MA/cm.sup.2 ", Appl. Phys. Lett. 63(13), (1993), pp. 1848-1850, discusses optimizing electrical performance in a high-T.sub.c superconducting ceramic by depositing it as a c-axis textured thin film on a crystalline substrate with a similar crystal structure and a buffer layer on its deposition surface.
Performance is optimized in the ceramic when it is deposited as a c-axis textured thin film on a crystalline substrate. This configuration cannot be used in many relevant device applications that require geometrically shaped or mechanically flexible ceramic in large dimensions. Recent efforts have been made to adapt thin film processing technologies to make c-axis textured ceramic thick films on metal substrates. These composite structures have achieved high electrical current performance by first depositing a buffer layer on a flexible metal substrate that has the same or similar crystal structure as the high-T.sub.c superconducting ceramic:
P-8
X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter, and D. E. Peterson, "High Current YBa.sub.2 Cu.sub.3 O.sub.7-.delta. Thick Films on Flexible Nickel Substrates With Textured Buffer Layers", Applied Physics Letters 65(15) (1994) pp. 1961-1963, demonstrates high critical current superconducting ceramic can be obtained using ion beam assisted deposition on a c-axis textured yttria-stabilized zirconia buffer layer deposited using the same process on nickel substrate.
P-9
P. Arendt, S. Foltyn, X. Wu, J. Townsend, C. Adams, M. Hawley, P. Tiwari, M. Maley, J. Willis, D. Moseley, Y. Coulter, "Fabrication of Biaxially Oriented YBCO On (00l) Biaxially Oriented Yttria-Stabilized Zirconia On Polycrystalline Substrates", MRS Symposium Proceedings on Epitaxial Oxide Thin Films and Heterostructures, MRS Bulletin 341 (1994) discusses using ion-assisted, ion-beam sputter deposition to obtain (00l) biaxially oriented films of cubic yttria-stabilized zirconia on polycrystalline metal substrates on to which yttrium-barium-copper-oxide superconducting ceramic is then heteroepitaxially deposited via pulse laser deposition.
References P-7 to P-9 cited above demonstrate the ability to apply modem processing technologies to improve characteristic performance in ceramics that are orientation sensitive. All modem techniques apply the ceramic to a metal substrate by first depositing a textured ceramic buffer layer on the metal. The buffer layer must have the same or similar crystalline structure to the ceramic layer whose properties are essential to the proper functioning of the device. The presence of the electrically insulating buffer layer is harmful to the proper functioning of a device when it is necessary to achieve ohmic contact between the textured ceramic and the metal on to which it is deposited. In the case of superconductors cited above, this is of particular importance when making wire that is subsequently wound into solenoid magnets. It is now well known that it is necessary to have the superconductor in intimate contact with a high thermal and electrical conductivity metal to stabilize the performance of a superconducting magnet:
P-10
Martin N. Wilson, "Superconducting Magnets", Oxford University Press, New York (1983) discusses the importance of placing the superconductor in intimate contact with a metal to achieve optimal performance in a superconducting magnet.
Another limitation of applying film technology to the production textured ceramic devices is the limited thickness to which the ceramic can be made, 10 microns or less. Since electrical capacity scales with the cross-sectional area of the current conductor, the ultimate performance of these devices will be limited to a maximum current load. Furthermore, it is not possible to apply these structures to making multiple filamentary wires, since they consist of a metal substrate, an electrically insulating buffer layer, and a superconducting ceramic as a discrete continuous strip. More robust ceramic thickness is possible in composites using bulk processing techniques. These include billet-processing using the oxide-powder-in-tube or metal precursor methods:
P-11
K. H. Sandhage, G. N. Riley, Jr., and W. L. Carter, Journal of Metals (43) (1991) p. 21, discusses preparing bismuth cuprate superconducting wire by grinding, milling, and reacting oxide powders, packing the blend into a silver tube that is sealed at both ends, deforming the billet into wire, and reacting the packed powders into a superconducting phase of the ceramic.
P-12
A. Otto, C. Craven, D. Daly, G. R. Podtburg, J. Schrieber, and L. J. Masur, Journal of Metals 45 (1993) p. 48 discusses packing elemental metal precursors to the ceramic in a silver tube, extruding the billet into wire, and reactively oxidizing the elemental metal precursor into superconducting phases of the ceramic.
These two techniques allow ceramic to be made into filamentary components and to bulk continuous dimensions, but have several practical limitations. Since the ceramic precursor is packed within a sealed silver tube and reacted, these techniques do not allow c-axis textured ceramic to be produced with an exposed ceramic surface, if so desired. The steps of grinding and pulverizing the precursor powders prior to reacting them into ceramic is both time and energy intensive. Grinding and milling steps are also susceptible to material degradation due to abrasive contact with grinding machinery metal and the associated risk of erosion material contamination. Furthermore, these processes have not demonstrated an ability to consistently make uniform high quality textured ceramic.
Fully crystallized ceramic is not normally reactive with metal surfaces. Crystallized ceramic, including bulk c-axis textured ceramic, can be bonded to metal substrates to leave an exposed ceramic oxide surface:
P-13
V. A. Maroni, "Method of Bonding Metals to Ceramics", U.S. Pat. No. 5,010,053, issued Apr. 23, 1991.
Other relevant background to this invention is contained in:
P-14
J. S. Luo, N. Merchant, E. J. Escorcia-Aparicio, V. A. Maroni, B. S. Tani, W. L. Carter, and G. N. Riley, Jr., "Composition and microstructural evolution of nonsuperconducting phases in silver-clad (Bi,Pb).sub.2 Sr.sub.2 CaCu.sub.2 O.sub.x composite conductors", Journal of Materials Research vol. 9, no. 12, (1994) pp. 3059-3067 discloses processing regimes that promote the growth of electrically insulating phases of bismuth cuprate ceramic.
Related Patents and Publications
The following prior art is deemed relevant to this invention. The disclosures relate generally to the use of metalorganic solutions that comprise metal precursors to a pertinent ceramic composition as salts of a carboxylic acid, and 2-ethylhexanoic acid in particular; or to the use of spray deposition techniques as a method to apply the ceramic precursor solution to a substrate. The first record publicly disclosing the use of a solution of 2-ethylhexanoate salts that comprise metal precursors to a RE-AE-Cu--O superconducting ceramic on yttria-stabilized zirconia was made by Nasu et al.:
P-15
H. Nasu, S. Makida, T. Kato, Y. Ibara, T. Imura, and Y. Osaka, "Superconducting Y--Ba--Cu--O Films with T.sub.c &gt;70 K Prepared by Thermal Decomposition Technique of Y--, Ba--, and Cu-2ethylhexanoates", Chemistry Letters, The Chemical Society of Japan, (1987), pp. 2403-2404, discloses the use of a carboxylic acid salt solution to prepare a superconducting ceramic on yttria-stabilized zirconia.
P-16
H. Nasu, S. Makida, T. Imura, and Y. Osaka, "Ba.sub.2 YCu.sub.3 O.sub.x films with T.sub.c (end)&gt;80 K prepared by the pyrolysis of 2-ethylhexanoates", Journal of Materials Science Letters 7 (1988) pp.858-866, discloses annealing treatments that improve the quality of superconducting ceramic thin films prepared on yttria-stabilized zirconia.
Both these references disclose the formation of a RE-AECu--O ceramic film on a substrate of similar crystalline structure. The precursors are applied to the substrate by first forming a liquid film coating, either by screen-printing or dip-coating techniques. The liquid film coating is then pyrolyzed into an amorphous oxide and then a crystalline oxide film using subsequent annealing steps.
Art remarkably similar to that disclosed by Nasu et al., and similar in some respects to this invention, has been recognized in patents issued by the United States Patent and Trademark Office:
P-17
J. M. Mir, J. A. Agostinelli, D. L. Peterson, G. R. Paz-Pujalt, B. J. Higberg, G. Rajeswarn, "Metalorganic deposition process for preparing superconducting oxide films", U.S. Pat. No. 4,880,770, issued Nov. 14, 1989.
P-18
J. A. Agostinelli, G. R. Paz-Puljalt, A. K. Mehrotra, L.-S. Hung, "Metalorganic deposition process for preparing heavy-pnictide superconducting oxide films", U.S. Pat. No. 4,950,643, issued Apr. 21, 1990.
Mir et al. (P-17) claim a method to prepare articles containing an electrically conductive rare-earth alkaline earth copper oxide (RE-AE-Cu--O) layer and processes for their preparation using a mixed metalorganic precursor. Agostinelli et al. (P-18) claim a method to prepare articles containing an electrically conductive heavy-pnictide mixed alkaline earth copper oxide (HP-AE-Cu--O) layer and processes for their preparation using a mixed metalorganic precursor. Heavy-pnictides are defined as the elements bismuth (Bi) and antimony (Sb), with the inclusion of small concentrations of lead (Pb).
Both these patents, as well as other related commonly assigned patents claim the same steps whereby which the patented articles are formed. In Step "A", a liquid coating of metalorganic precursors to the ceramics is applied to a substrate by passing the substrate through a reservoir of the solution comprised of metalorganic precursors to the ceramic dissolved in a film forming solvent. The application of a liquid coating is specifically defined as a distinct processing step that cannot be combined with subsequent processing steps. Subsequent processing steps are defined as (Step "B") comprising a heat treatment that pyrolyzes the liquid coating into an amorphous coating on the substrate; a further heat treatment (Step "C") that decomposes carbonate phases that result in the thermal decomposition of alkaline earth metal ligands and converts the amorphous oxide layer into a more electrically conducting crystalline form; a cooling treatment (Step "D") that reduces the applied heat from crystallization temperature(s) to 500.degree. C. (preferably 200.degree. C.) to form a rigid crystalline layer on the substrate; and a post-anneal (Step "E") in an oxygen-rich atmosphere to equilibrate the deposited crystalline layer. It is explicitly stated that only Steps "B" through "E" can be combined into a single processing step.
Agostinelli et al and Mir et al claim the use of spray deposition techniques to apply the precursors to the substrate, but only as a liquid coating. Agostinelli et al and Mir et al recognize the importance of c-axis texture in the crystallized layer, and acknowledge that crystallinity in the deposited layer can only be engendered if the ceramic coating is applied to a substrate of identical or similar crystalline structure. Agostinelli et al and Mir et al claim the use of substrates with similar or identical crystalline structures, and the use of such crystalline surfaces deposited as a barrier or buffer layer on substrates of dissimilar crystalline structure, including metal substrates. Agostinelli et al assert and claim that silver, used as the deposition surface, will promote c-axis orientation in the deposited ceramic layer even though it does not have a crystal structure that is compatible with the ceramic. Although Agostinelli et al claim the use of silver as a free-standing unitary substrate, and the use of an elongated silver substrate to produce superconductive articles of long length. This claim is not reduced practice. Agostinelli et al demonstrate HP-AE-Cu--O ceramic thin films on substrates of magnesium oxide (MgO), strontium titanate (SrTiO.sub.3), silicon (Si), fused quartz, and sapphire; and on barrier layers of zirconia (ZrO.sub.2) deposited on fused quartz, silicon, sapphire, and silicon dioxide (SiO.sub.2) on silicon. Mir et al demonstrate the preparation of RE-AECu--O ceramic films on strontium titanate, copper, and glass fiber, but make no reference to controlling c-axis texture in the deposited layer.
Recent investigations into the art have shown that the appearance of c-axis texture in ceramic formed at a silver interface is due to a reaction-induced mechanism in the phase conversion of (Bi,Pb).sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8 and Bi.sub.1.80 Pb.sub.0.40 Sr.sub.1.91 Ca.sub.2.03 Cu.sub.3.06 O.sub.10-.delta. bismuth cuprate ceramic:
P-19
J. S. Luo, N. Merchant, V. A. Maroni, W. L. Carter, and G. N. Riley, Jr., Applied Physics Letters 61, (1992) p. 690 discloses the phenomenon of reaction-induced texture.
P-20
P. E. D. Morgan, J. D. Piche, and R. M. Housely, Physica C 191, (1992), p. 179, discloses evidence for a silver containing eutectic liquid that promotes the "solution reprecipitation" of Bi.sub.1.80 Pb.sub.0.40 Sr.sub.1.91 Ca.sub.2.03 Cu.sub.3.06 O.sub.10-.delta. phase ceramic.
These studies show that silver actually participates in the reaction of bismuth cuprate (HP-AE-Cu--O) ceramic, acting as a catalyst that increases the rate of reaction. Bismuth cuprate ceramic will produce an accelerated growth front when reacted in contact with a silver interface. Growth will expand in directions where the ceramic is free to flow or experiences comparable reaction kinetics. As such, silver substrates by themselves do not assure c-axis texture unless silver is used as an interfacial layer between bismuth cuprate ceramic and a substrate of compatible crystalline structure. These facts are now well known.
References P-7 through P-9 clearly show that extraordinary measures must be taken to produce c-axis oriented films thicker than 0.5 micron even on single crystal surfaces. Evidence is now widely reported that ceramic layers deposited on silver substrates will not produce c-axis oriented films without mechanical texturing steps added to the process:
P-21
L. P. de Rochemont, V. A. Maroni, M. Klugerman, R. J. Andrews, and W. C. Kelliher, "Fabricating Multifilamentary Bismuth Cuprate Tapes by Metalorganic Spray Pyrolysis", Applied Superconductivity vol. 2, no. 3/4 (1994) pp. 281-294 discloses that bulk ceramic coatings formed by pyrolyzing 2-ethylhexanoate precursor salts do not have c-axis orientation, and that c-axis texture is only induced by multiple mechanical swaging steps incorporated into the reaction process between thermal processing steps.
Neither Agostinelli et al nor Mir et al demonstrate that c-axis oriented ceramic can be formed on a unitary silver substrate, nor do they claim the use of thermomechanical processing steps to endow a ceramic deposited on silver with c-axis texture. Given recent developments to the art it cannot be claimed that c-axis orientation is an obvious extension of pyrolyzing ceramic from liquid coated metalorganic precursors on the surface of a silver substrate.
Agostinelli et al and Mir et al only claim methods to produce articles coated with ceramic layers that are 1.5 and 1.0 micron thick or less, respectively. If it is desirous to achieve ceramic layers with thickness greater than 1.0 and 1.5 micron it is necessary to repeat the processing steps "A" through "E", as defined by Agostinelli et al and Mir et al.
DeSisto et al (P-22) disclose the pyrolysis of metalorganic precursors to a RE-AE-Cu--O ceramic on a dielectric magnesium oxide (MgO) substrate heated to 430.degree. C. and subsequent annealing.
P-22
W. J. DeSisto, R. L. Henry, M. Osofsky, and J. V. Marzik, "YBa.sub.2 Cu.sub.3 O.sub.7-.delta. thin films deposited by an ultrasonic nebulization and pyrolysis method", Thin Solid Films, 206 (1991) pp.128-131, discloses the formation of a RE-AE-Cu--O thin film by pyrolyzing metalorganic precursors in an alcohol by spraying the solution onto a heated dielectric substrate. MgO has identical or similar crystal structure to the deposited ceramic. Thin films with c-axis orientation are reported, but only in films with thickness of 0.5 micron or less, which is consistent with the finding that these ceramic thin films flip their orientations at a thickness of .about.0.5 micron from c-axis oriented to a-axis oriented even on compatible single crystal substrates (P-7). DeSisto et al do not demonstrate that a c-axis oriented ceramic coating can be formed on a metal substrate with non-compatible crystal structure, nor is the use of mechanical texturing steps between thermal processing treatments disclosed. DeSisto et al use solutions comprising volatile metal precursor derivatives of 2,2,6,6,-tetramethyl-3,5-heptanedione and 1-butanol as a solvent, rather than a solution of carboxylic acid salts.
Neither DeSisto et al, nor Agostinelli et al, nor Mir et al disclose methods to prepare carboxylic acid salt precursor solutions that reduce the formation of alkaline earth carbonate phases in subsequently spray pyrolyzed deposits. Neither DeSisto et al, nor Agostinelli et al, nor Mir et al disclose and demonstrate methods to prepare bulk c-axis oriented ceramic layers with thickness in excess of 2.5 micron on metal substrates with or without a buffer, barrier, or surface layer that has compatible crystal structure to the ceramic.